Interpretive Summary: Staphylococcus aureus is a Gram-positive bacterium that can be commonly found on the skin or in the nasal passages of most humans and animals. It has been implicated in a number of diseases in humans ranging from minor skin infections to more serious infections such as pneumonia. Studies have shown that humans shed S. aureus onto surfaces in their environment (including water) and that this is a source of spread to other individuals. Reports of S. aureus detected in marine environments have occurred since the early 1990’s. In this study, S. aureus from marine waters and sand at a subtropical recreational beach, with and without bathers present, were characterized in order to investigate possible sources and to identify the risks to bathers of exposure to these organisms. Over a period of 17 months, 1001 water and 36 intertidal sand samples were collected by either bathers or investigators at a subtropical recreational beach. Methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) were isolated, identified, and characterized using molecular methods. Both MSSA and MRSA were isolated from the sources and some MRSA were genetically related to the community-associated MRSA (CA-MRSA) strain, USA300. There was a significant correlation between the daily average number of bathers and all S. aureus in the water. These results indicate that CA-MRSA found in waters and sand at a subtropical recreational beach were clonally related or highly similar, and the presence of S. aureus in these waters correlated with the daily average number of bathers in the water. This report directly addresses humans bathing in a marine environment and S. aureus in the water and supports the concept that humans are a potential direct source for S. aureus in marine waters. Researchers can use this information to evaluate sources of environmental contamination and in designing strategies to reduce microbial contamination of the environment.

Technical Abstract:
Reports of Staphylococcus aureus detected in marine environments have occurred since the early 1990’s. This investigation sought to isolate and characterize S. aureus from marine waters and sand at a subtropical recreational beach, with and without bathers present, in order to investigate possible sources and to identify the risks to bathers of exposure to these organisms. During 40 days over 17 months, 1001 water and 36 intertidal sand samples were collected by either bathers or investigators at a subtropical recreational beach. Methicillin sensitive (MSSA) and methicillin-resistant S. aureus (MRSA) were isolated and identified using selective growth media and an organism-specific molecular marker. Antimicrobial susceptibility, staphylococcal cassette chromosome mec (SCCmec) type, pulsed-field gel electrophoresis (PFGE) pattern, multi-locus sequence type (MLST), and staphylococcal protein A (spa) type were characterized for all MRSA. 1334 MSSA isolates were obtained from 248 bather water, 102 ambient water, and 9 sand samples on 37 days. Twenty-two MRSA were isolated from seven bather water, two ambient water, and three sand samples from ten collection days. Based on PFGE results, 17 of 22 were clonally related to the community-associated MRSA strain USA300. MRSA isolates were all SCCmec type IVa, encompassed five spa types (t008, t064, t622, t688, t723), two MLST types (ST008 and ST005), and 21 of 22 isolates carried the genes for Panton-Valentine leukocidin (PVL). There was a significant correlation (r=0.45; p=0.05) between the daily average number of bathers and S. aureus in the water. Within the sand environment, S. aureus was isolated more often from above the intertidal zone than from 80 intermittently wet or inundated sand. These results indicate that CA-MRSA found in waters and sand at a subtropical recreational beach were clonally related or highly similar, and the presence of S. aureus in these waters correlated with the daily average number of bathers in the water. This report directly addresses human use in a marine environment and S. aureus in the water and supports the concept that humans are a potential direct source for S. aureus in marine waters.